TWI644422B - Semiconductor memory device - Google Patents

Abstract

The semiconductor memory device according to the embodiment includes a first wiring extending in the first direction, a second wiring extending in a second direction intersecting the first direction, and an intersection disposed between the first wiring and the second wiring In the memory cell of the unit, the memory cell has a first film in which electrical resistance changes in a third direction intersecting the first and second directions, a second film having conductivity, and an insulating property. 3 membranes.

Description

Semiconductor memory device

Embodiments of the present invention relate to a semiconductor memory device.

As a semiconductor memory device that replaces a low-cost and large-capacity known flash memory, there is a variable resistance memory (ReRAM: Resistance RAM) in which a memory cell is a variable resistance film. ReRAM can form an intersection type memory cell array, so that it can achieve the same large capacity as flash memory. Further, in order to further increase the capacity, a ReRAM having a so-called VBL (Vertical Bit Line) structure in which a bit line of a selected wiring is arranged in a vertical direction with respect to a semiconductor substrate has been developed.

The semiconductor memory device according to the embodiment includes a first wiring extending in the first direction, a second wiring extending in a second direction intersecting the first direction, and an intersection disposed between the first wiring and the second wiring The memory cell has a first film in which a resistance is electrically changed in a third direction intersecting the first and second directions, a second film having conductivity, and a third insulating property. membrane. According to the embodiment, it is possible to provide a semiconductor memory device capable of reducing dielectric breakdown of an insulating film of a memory cell during a forming operation.

Hereinafter, a semiconductor memory device according to an embodiment will be described with reference to the drawings. First, the overall configuration of the semiconductor memory device of the embodiment will be described. Fig. 1 is a view showing a functional block of a semiconductor memory device according to an embodiment. As shown in FIG. 1, the semiconductor memory device of the embodiment includes a memory cell array 1, a column decoder 2, a row decoder 3, an upper block 4, a power supply 5, and a control circuit 6. The memory cell array 1 includes a plurality of word line lines WL and a plurality of bit line lines BL, and a plurality of memory cells MC selected on the word line lines WL and the bit lines BL. The column decoder 2 selects the word line WL at the time of the access operation. The row decoder 3 selects the bit line BL during the access operation and includes a driver that controls the access action. The upper block 4 selects the memory cell MC as the access target in the memory cell array 1. The upper block 4 assigns a column address and a row address to the column decoder 2 and the row decoder 3. When the data is written/read, the power supply 5 generates a combination of predetermined voltages corresponding to the respective operations, and supplies them to the column decoder 2 and the row decoder 3. The control circuit 6 performs control such as transmitting an address to the upper block 4 in accordance with a command from the outside, and controls the power source 5. Next, an outline of the memory cell array 1 will be described. 2 is a circuit diagram of a memory cell array of a semiconductor memory device of an embodiment. As shown in FIG. 2, the memory cell array 1 includes a plurality of word lines WL extending in the X direction, a plurality of bit lines BL extending in the Z direction, and a plurality of word lines WL and a plurality of bit lines. A plurality of memory cells MC at the intersection of BL. Moreover, the memory cell array 1 has a plurality of global bit lines GBL. The bit lines BL arranged in the Y direction among the plurality of bit lines BL are commonly connected to one global bit line GBL via the selection transistor STR. Each of the selection transistors STR is controlled by a selection gate line SG. Next, the structure of the memory cell array 1 will be described. 3 is a perspective view of a memory cell array of a semiconductor memory device of an embodiment. In the configuration of Fig. 3, an interlayer insulating film or the like of one portion of the memory cell MC or wiring is omitted. 4 is a cross-sectional view in the YZ direction of the periphery of the memory cell of the memory cell array of the semiconductor memory device. As shown in FIG. 3, the memory cell array 1 has a so-called VBL (Vertical Bit Line) structure in which the bit line BL extends perpendicularly to the principal plane of the semiconductor substrate SS. That is, the plurality of word line lines WL are arranged in a matrix in the Y direction and the Z direction, and respectively extend in the X direction. The plurality of bit lines BL are arranged in a matrix in the X direction and the Y direction, and extend in the Z direction. Further, each of the memory cells MC is disposed at each of the intersections of the plurality of word line lines WL and the plurality of bit lines BL. That is, a plurality of memory cells MC are arranged in a three-dimensional matrix in the X direction, the Y direction, and the Z direction. Here, the word line WL is formed of, for example, titanium nitride (TiN) or tungsten (W). The bit line BL is formed of, for example, poly-Si. Between the semiconductor substrate SS and the plurality of bit lines BL, a plurality of global bit lines GBL arranged in the X direction and extending in the Y direction are disposed. Furthermore, the global bit line GBL may not be disposed directly above the semiconductor substrate SS, and other elements or the like may be interposed between the global bit line GBL and the semiconductor substrate SS. For example, a circuit such as a CMOS element can be formed on the semiconductor substrate SS, and a global bit line GBL is provided thereon. Furthermore, a selective transistor STR is disposed at a lower end of the plurality of bit lines BL, respectively. The selection transistors STR are controlled by a plurality of selection gate lines SG arranged in the Y direction and extending in the X direction. In the case of Fig. 3, a plurality of selection transistors STR arranged in the X direction are controlled by one selection gate line SG, and on the other hand, selection transistors STR arranged in the Y direction are individually controlled. Moreover, the transistor STR does not necessarily have to be located at the lower end of the bit line BL, and may be located above the word line WL or the bit line BL. In the following description, a semiconductor memory device having a memory cell array 1 having a VBL structure as shown in FIG. 3 will be described as an example. However, it should be noted that the present embodiment can be widely applied to arranging memory cells MC in the X direction and the Y direction. A semiconductor memory device using a memory cell MC having a variable resistive film or the like in the case of expanding a two-dimensional matrix shape. As shown in FIG. 4, the memory cell MC has a variable resistance film VR, a conductive film CF, and an insulating film IF which are sequentially arranged in the Y direction. Here, the variable resistance film VR is formed of a material whose electrical resistance changes electrically, for example, by hafnium oxide (HfO ₂ ). The conductive film CF is formed of, for example, a metal such as titanium nitride (TiN) or tungsten (W). The insulating film IF is a film which imparts a non-linear current-voltage characteristic (hereinafter referred to as "IV characteristic") to the memory cell MC, and is formed, for example, of yttrium oxide (SiO ₂ ). The memory cell array 1 includes, in addition to the configuration shown in FIG. 3, an interlayer insulating film 101 disposed between the respective word lines WL. Further, the side surface of each of the word lines WL in the Y direction is more recessed in the Y direction than the side surface of the interlayer insulating film 101 in the Y direction (portion a101 shown in FIG. 4). The conductive film CF and the insulating film IF of the memory cell MC are disposed at the portion a101. The variable resistance film VR of the two memory cells MC adjacent in the Z direction is integrally formed along the side surface of the bit line BL facing the second direction. The conductive film CF of the two memory cells MC adjacent in the Z direction is separated between the two memory cells MC. The side surface of the conductive film CF facing the Y direction is in contact with the variable resistance film VR at a position in the Z direction which is the same as the word line WL. The insulating film IF of the two memory cells MC adjacent in the Z direction is integrally formed. In the portion a101, the insulating film IF is disposed between the predetermined word line WL and the two interlayer insulating films 101 and the conductive film CF which are interposed between the predetermined word lines WL in the Z direction. Further, the insulating film IF is disposed in contact with a side surface and an upper surface in the Y direction of one of the two interlayer insulating films 101, a side surface in the Y direction of the predetermined word line WL, and the two The other bottom surface of the interlayer insulating film 101 and the side surface facing the Y direction. Further, the side surface of the insulating film IF facing the Y direction and the side surface of the conductive film CF facing the Y direction are disposed in the same plane. Further, the side surface of the insulating film IF facing the Y direction is in contact with the variable resistance film VR at a position in the Z direction which is the same as that of the interlayer insulating film 101. Furthermore, the insulating film IF does not necessarily have to be integrated between the memory cells MC adjacent in the Z direction, and may be separated between the memory cells. Next, the effect of the memory cell MC having the above structure will be described. Fig. 5 is a cross-sectional view showing the effect of the conductive film of the memory cell of the semiconductor memory device of the embodiment. Further, Fig. 6 is a graph showing the IV characteristics of the memory cells of the semiconductor memory device. In the access operation to the memory cell MC, in addition to the address operation for converting the resistance state of the variable resistance film VR, there are a read operation and a formation operation. The read operation of the memory cell MC senses the resistance state of the variable resistance film VR, for example, by applying a predetermined read voltage Vcell=Vr to the selected memory cell MC. At this time, it is measured that the cell current Icell of the selected memory cell MC flows. At this time, a voltage of, for example, Vcell=Vr/2 or less is applied to the non-selected memory cell MC so that a large cell current Icell does not flow. In order to realize the readout operation with low power consumption, the memory cell MC is required to have a nonlinear IV characteristic, that is, for example, as shown by a dot chain line in FIG. 6, when selected (that is, when the readout voltage Vell=Vr is applied) A cell current Icell sufficient for data sensing is passed, and when not selected (that is, when a voltage of Vcell=Vr/2 or less is applied), only a cell current Icell as small as possible flows. The formation operation of the memory cell MC is an operation performed immediately after the manufacture of the memory cell MC, and is an operation in which the variable resistance film VR forms a filament path. Thereby, the resistance state of the variable resistance film VR can be stably changed. This formation operation can be realized by applying a higher formation voltage to the memory cell MC than the write voltage used in the write operation. Here, the following aspects must be noted in the above forming operation. That is, during the forming operation, a forming voltage is applied to the memory cell MC, but once the filament path is formed in the variable resistive film VR, most of the forming voltage is applied to the memory cell MC other than the variable resistive film VR. section. Here, assuming that the conductive film CF is not present in the memory cell MC, the voltage is directly applied to the insulating film IF, and in the worst case, the insulating film IF may cause dielectric breakdown. As a result, the nonlinearity of the IV characteristic of the memory cell MC secured by the insulating film IF is linear as shown by the broken line in FIG. 6, and the cell current Icell flowing through the non-selected memory cell MC increases during the readout operation. . In this embodiment, in the memory cell MC of the embodiment, the conductive film CF is provided between the variable resistance film VR and the insulating film IF. Further, by the resistance component of the conductive film CF, the voltage applied to the insulating film IF at the time of forming the filament path is alleviated. As a result, the insulating film IF is less likely to cause dielectric breakdown, and as shown by the solid line in Fig. 6, it is easy to maintain the nonlinearity of the IV characteristic of the memory cell MC. Thereby, of course, the cell current Icell flowing through the non-selected memory cell MC during the read operation is significantly reduced as compared with the case where the insulating film IF is insulated and broken (the hollow arrow in FIG. 6). Further, in order to obtain a larger buffering effect in the above forming operation, it is desirable that the conductive film CF has a certain thickness with respect to the current path (Y direction in FIG. 4). For example, as shown in FIG. 4, the thickness Wcf of the conductive film CF in the Y direction is made thicker than the thickness Hcf of the conductive film CF in the Z direction (or the thickness in the X direction not shown), or a variable resistance film. The thickness Wvr of the VR in the Y direction is thicker. Next, the manufacturing steps of the memory cell array 1 will be described. Figs. 7 to 13 are perspective views showing the YZ direction of the manufacturing steps of the memory cell array of the semiconductor memory device of the embodiment. First, as shown in FIG. 7, a plurality of interlayer insulating films 101 and a conductive film 102 are alternately laminated on a semiconductor substrate (not shown). Here, the interlayer insulating film 101 is formed of, for example, yttrium oxide (SiO ₂ ). The conductive film 102 is formed of, for example, titanium nitride (TiN) or tungsten (W), and functions as a word line WL. Then, as shown in FIG. 8, by the anisotropic etching, at least the groove 121 extending in the X direction is formed from the upper surface of the uppermost interlayer insulating film 101 to the bottom surface of the lowermost interlayer insulating film 101. Then, as shown in FIG. 9, the end portion of the conductive film 102 exposed to the trench 121 is recessed by the isotropic etching through the trench 121 (portion a101). Then, as shown in FIG. 10, an insulating film 103 is formed on the side surface of the trench 121. Thereby, the insulating film 103 is in contact with the side surface and the upper surface of the interlayer insulating film 101 disposed on the lower side of the predetermined conductive film 102 where the portion a101 is exposed on the lower surface of the trench 121, and the orientation of the predetermined conductive film 102. The side surface of the Y direction and the bottom surface of the interlayer insulating film 101 disposed on the upper side of the predetermined conductive film 102 and the side surface facing the Y direction. Here, for example, an insulating film 103 (SiO ₂₎ is formed of silicon oxide, and IF functions as an insulating film. Then, as shown in FIG. 11, the conductive film 104 is formed on the trench 121 in which the insulating film 103 is formed, and the conductive film 104 is filled in the portion a101. Here, the conductive film 104 is formed of, for example, a metal such as titanium nitride (TiN) or tungsten (W), and functions as the conductive film CF. Then, as shown in FIG. 12, the conductive film 104 is removed in such a manner that the conductive film 104 is separated from the interlayer insulating film 102 at the same position in the Z direction by anisotropic etching through the trench 121 until the insulating film 103 is used. The side facing the Y direction is exposed. Then, as shown in FIG. 13, the variable resistance film 105 is formed on the side surface of the trench 121 on which the insulating film 103 and the conductive film 104 are formed. Here, the variable resistance film 105 is formed of a material whose electrical resistance changes electrically, and is formed, for example, of hafnium oxide (HfO ₂ ). The variable resistance film 105 functions as the variable resistance film VR. Finally, the conductive film 106 is formed on the trench 121 in which the variable resistance film 105 is formed. The conductive film 106 is formed of, for example, poly-Si and functions as a bit line BL. The memory cell array 1 shown in Fig. 4 is formed by the manufacturing steps described above. As described above, according to the embodiment, it is possible to provide a semiconductor memory device in which the dielectric breakdown of the insulating film of the memory cell generated during the forming operation is reduced. [Others] The embodiments of the present invention have been described above, but the embodiments are presented as examples and are not intended to limit the scope of the invention. The various embodiments of the invention can be embodied in a variety of other forms, and various omissions, substitutions and changes can be made without departing from the scope of the invention. The invention or its modifications are intended to be within the scope and spirit of the invention and are intended to be included within the scope of the invention. RELATED APPLICATIONS This application claims priority to US Provisional Patent Application No. 62/303,505 (filed on March 4, 2016) and US Patent Application No. 15/074,395 (Application Date: March 18, 2016) . The present application contains the entire contents of the basic application by reference to these basic applications.

1‧‧‧ memory cell array

2‧‧‧ column decoder

3‧‧‧ row decoder

4‧‧‧Upper block

5‧‧‧Power supply

6‧‧‧Control circuit

101‧‧‧Interlayer insulating film

102, 104, 106, CF‧‧‧ conductive film

103‧‧‧Insulation film

105‧‧‧Variable Resistive Film

121‧‧‧ trench

A101‧‧‧ parts

BL‧‧‧ bit line

GBL‧‧‧Global Bit Line

Hcf, Wcf, Wvr‧‧‧ thickness

IF‧‧‧Insulation film

MC‧‧‧ memory cell

SG‧‧‧Selected gate line

SS‧‧‧Semiconductor substrate

STR‧‧‧Selecting a crystal

VR‧‧‧Variable Resistive Film

WL‧‧‧ character line

Fig. 1 is a view showing a functional block of a semiconductor memory device according to an embodiment. 2 is a circuit diagram of a memory cell array of a semiconductor memory device of an embodiment. Fig. 3 is a schematic perspective view showing a memory cell array of the semiconductor memory device of the embodiment. Fig. 4 is a cross-sectional view showing the vicinity of a memory cell of a memory cell array of the semiconductor memory device of the embodiment. Fig. 5 is a cross-sectional view showing the effect of the conductive film of the memory cell of the semiconductor memory device of the embodiment. Fig. 6 is a graph showing current-voltage characteristics of a memory cell of the semiconductor memory device of the embodiment. 7 to 13 are cross-sectional views showing the steps of manufacturing the memory cell array of the semiconductor memory device of the embodiment.

Claims (20)

A semiconductor memory device including: a first wiring extending in the first direction; a second wiring extending in a second direction intersecting the first direction; and an intersection disposed between the first wiring and the second wiring a memory cell having a first film, a second conductive film, and an insulating layer which are electrically connected to each other in a third direction intersecting the first and second directions; 3 membranes. The semiconductor memory device of claim 1, wherein a thickness of the third film in the third direction is thicker than a thickness of at least one of the first direction and the second direction of the second film. The semiconductor memory device of claim 1, wherein the first film contains hafnium oxide (HfO ₂ ). The semiconductor memory device of claim 1, wherein the second film contains a metal. The semiconductor memory device of claim 1, wherein the third film contains cerium oxide (SiO ₂ ). The semiconductor memory device of claim 1, wherein the first film has a filament. A semiconductor memory device comprising: a semiconductor substrate extending in first and second directions intersecting each other; a plurality of strips extending in a third direction intersecting the first and second directions and extending in the first direction a wiring, a second wiring extending in the third direction, and a plurality of memory cells disposed at an intersection of the plurality of first wirings and the second wiring; one of the memory cells having a layer along the second direction The first film having electrical resistance changes, the second conductive film, and the third insulating film. The semiconductor memory device according to claim 7, wherein the thickness of the second film in the second direction is thicker than the thickness of at least one of the first direction and the third direction of the second film. The semiconductor memory device of claim 7, wherein the thickness of the second film in the second direction is thicker than the thickness of the first film in the second direction. The semiconductor memory device of claim 7, wherein the first film contains hafnium oxide (HfO ₂ ). The semiconductor memory device of claim 7, wherein the second film contains a metal. The semiconductor memory device of claim 7, wherein the third film contains cerium oxide (SiO ₂ ). The semiconductor memory device of claim 7, wherein the first film has a filament. The semiconductor memory device of claim 7, wherein the first film of the two memory cells adjacent in the third direction is integrated. The semiconductor memory device of claim 7, wherein the second film of the two memory cells adjacent in the third direction is separated between the two memory cells. The semiconductor memory device of claim 7, wherein the third film of the two memory cells adjacent in the third direction is integrated. The semiconductor memory device of claim 7, further comprising: a first insulating film disposed between the two first wirings adjacent to each other in the third direction; and a side surface of the two first wirings facing the second direction The side surface facing the second direction of the first insulating film is further recessed in the second direction. The semiconductor memory device of claim 7, further comprising two first insulating films interposed between the first wiring in the third direction, wherein the third film is in contact with one of the two first insulating films The side surface and the upper surface facing the second direction, the side surface of the first wiring facing the second direction, and the other bottom surface of the two first insulating films and a side surface facing the second direction. The semiconductor memory device according to claim 7, wherein the side surface of the second film facing the second direction and the side surface of the third film facing the second direction are disposed in the same plane. The semiconductor memory device of claim 7, further comprising: a first insulating film disposed between the two adjacent first wirings in the third direction, wherein the first film is the same as the first insulating film The position in the three directions is in contact with the third film described above.